The invention relates to a fluid friction clutch of the type used to drive colling air fans in vehicle cooling systems and the like. A fluid friction clutch of this type is known from German Published Unexamined Application (DE-OS) 32 26 634. In this construction, in the area of the outer circumference of the clutch disk, a damming body provided with guiding surfaces is assigned to the front side of the working chamber and is located in front of an overflow opening leading to the storage chamber. In this case, the damming body projects into a surrounding groove of the clutch disk in which the clutch oil collects at this radially most exterior point. In the known construction, two damming bodies of this type are provided diametrically opposite at the circumference of the working chamber in order to increase the amount of the returned oil. By means of constructions of this type, a so-called modulating control can be achieved; i.e., a slow rise and fall of the rotational speed of the fan assigned to the clutch in the case of higher rotational speeds and in the case of a correspondingly higher rotational slip speed. However, it is a disadvantage that during idling or in the case of low rotational drive speeds, sudden rotational speed changes are caused by the fluid friction clutch, which generally is called a "surging" of the clutch.
It is an objective of the present invention to find a development of a fluid friction clutch of the initially mentioned type by means of which a modulating control can be achieved also in the case of low rotational speeds.
For achieving this objective, damming and guide means are provided for forcing supply of clutch fluid to both sides of the disk. By means of this development, it is ensured that the clutch fluid is, in a forced manner, always supplied to both sides of the clutch disk, so that also, in the case of low rotational speeds and therefore of a small circulating amount of fluid, the wetting of the working chamber is ensured on both sides of the clutch disk. By means of the invention, a forced guiding of the clutch fluid is achieved on both sides of the working chamber. By means of this development, a uniform power transmission can be achieved also in the low rotational speed range. There will be no "surging".
In advantageous embodiments of the invention an insert is inserted into a radial recess of the clutch dividing wall which insert accommodates a return flow duct for the clutch fluid. Preferred embodiments also have a damming body formed as a diagonally extending edge at the outer circumference of the clutch disk, which edge delimits the edge of a deflecting duct. These characteristics permit a simple implementation of a fluid deflector which causes the desired deflection of the clutch fluid from the front working chamber first into the rear working chamber and from there, back into the storage chamber.
Preferred embodiments use a cylindrical shell of the disk as a sealing edge, which in a simple manner, provides the boundary between the front and the rear working chamber. Certain preferred embodiments use a housing projection as a damming body that borders on the rear side of the clutch disk providing a simple construction.
Other characteristics of preferred embodiments result in the significant advantage that the clutch disk and housing form a pumping system that contributes to the fact that the clutch fluid, in addition to the effect caused by centrifugal force, is supplied to the largest diameter. As a result, in the exterior area, where also the surrounding ring ducts are provided in the housing according to certain features of preferred embodiments, a pressure increase can be achieved. As a result, the working spaces can be emptied faster, and shorter hystereses occur for the clutch. At the same time, a stable oil ring is formed at the outer diameter which causes an extremely smooth movement of the clutch.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.